Author Topic: Truss Calculators  (Read 177967 times)

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Offline Medeek

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Re: Truss Calculators
« Reply #125 on: October 26, 2015, 07:29:24 PM »
Various configurations of a vaulted or cathedral truss:

Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #126 on: October 27, 2015, 08:00:15 AM »
Various configurations of dual pitch trusses:

Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #127 on: October 27, 2015, 08:58:13 PM »
Using the Medeek Truss Plugin and the housebuilder plugin I was able to create this simple model in about 3 minutes:



I would like to be able to create this type of model in the future:



This model was created in Solidworks and probably took a day or two to assemble.  Notice the gambrel attic and the gable end trusses.  That ability I would like to add into the plugin.

This next model was also created in Solidworks and only shows the foundation and framing, the entire model represents about a month of work including the drawing set.



I would like to see a plugin that is capable of generating this level of structural detail in a couple of hours instead of weeks.  Is this possible?
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #128 on: October 28, 2015, 01:51:09 AM »
I've got gable end trusses working for king post trusses:



I haven't made this latest update live just yet as I need to update all of the other truss types to make sure it does not break anything.

The other thing I am changing is the second user prompt box that allows one to enter in the number of trusses.  I have now switched to a building length and the logic spaces the trusses based on the this length and the truss on center spacing.  Gable end trusses can be switch on or off.  Spacing of the gable studs is another user input.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #129 on: October 29, 2015, 06:13:36 AM »
I would like to add in the gambrel attic type truss next but I need more examples of this truss type.  I've got a few configurations that I've used in my own designs but I am interested in any other designs that have been used recently by others.

In particular I am looking for large, clear spanning gambrel attic truss drawings or PDFs (shop drawings from a truss manufacturer).  I would be particularly interested in designs that integrate a floor truss into the bottom chord.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #130 on: November 02, 2015, 12:24:28 AM »
I've decided to post a page with my thoughts on the current state of truss software or the lack thereof:

http://design.medeek.com/resources/truss/study1/attictrussanalysis.html

This is my first draft so I may change it up some but the point really is my conclusion I draw at the end.  I really don't see why the Mitek's, Alpine etc... don't market a solution for engineers and architects.  Instead we rely on "technicians" to design our trusses and recently I have been very appalled by some of the designs I have seen lately.

Not to put down these folks, some of them are very good at what they do and those select individuals are definitely an asset to the construction community as a whole.

I don't have the resources or the man hours to program a solution that could possibly compete with their software.  However, it is my hope that by trying to pursue this route I can force their hand into offering a solution for engineers and in a sense commoditize their product.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #131 on: November 03, 2015, 10:28:35 PM »
Version 1.0.7 is now live.  The big improvement is the ability to click with the mouse at three corners and place the truss set without any additional rotating or translating.

In literally seconds I can now put a floor and a roof on 4 walls using the truss plugin and the Homebuilder plugin:



Of course the gable walls are not quite right but you get the idea.  I may have slightly misunderestimated (a word created by GW Bush) SketchUp and what one can do with it.
Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #132 on: November 04, 2015, 04:25:51 AM »
Wow! you are getting close to building with a few clicks. I'm assuming for a cut up roof you can fly in the truss groups and then hand draw the field framing.

I do agree with your comments in the previous post, the more we know, the more we know.

Offline Medeek

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Re: Truss Calculators
« Reply #133 on: November 05, 2015, 12:02:58 AM »
Version 1.0.8 - 11.04.2015
- Added Weyerhauser TJI® I-joists: 110, 210, 230, 360, 560, 560D.
- Rim joist option enabled for TJI floor joists.





Only a rectangular configuration is available currently.  If I can figure out how to code a polygon version of this that would be much more impressive (ie. pick the points that define the perimeter of the foundation and the plugin generates the complete floor layout).

This is straying a bit from trusses but I figured if I'm going to include floor trusses I might as well make floor joists available as well, just a small bit of code to get there.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline UK4X4

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Re: Truss Calculators
« Reply #134 on: November 05, 2015, 03:28:45 AM »
Your doing some awsome work, really coming along

Offline Medeek

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Re: Truss Calculators
« Reply #135 on: November 05, 2015, 11:09:48 PM »
Your doing some awsome work, really coming along

The thing with programming this plugin is it is easy to make rapid progress.  I can get tangible results without slogging through mountains of calculations, not to say that I don't enjoy programming my other calculators but this one seems a lot easier and progress is notable.

Version 1.0.9 - 11.05.2015
- Added separate toolbar icons for floor trusses and joists.
- Created separate submenu items under the Medeek Truss Plugin Extension for roof and floor trusses.

The main menu was getting a bit cluttered and not so user friendly so I split it out into "Roof" and "Floor", hopefully this makes more sense. 
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Truss Calculators
« Reply #136 on: November 06, 2015, 12:52:51 AM »
As I've been contemplating adding gambrel attic trusses to the truss plugin I've had to give some thought to what constitutes a good gambrel design.  I've looked into this before but my conclusion is that no matter the lower and upper pitch of the roof a good looking design seems to be always achievable if the lower and upper legs of the roof are more or less equal in the length.  To that end I've devised a simple spreadsheet calculator that will quickly throw out the numbers and display a graphic of the gambrel profile:



I'm not saying this is a hard and fast rule but it seems to give decent results.  Minor variations (ie. L1 not equal to L2) are generally okay but if one leg is significantly longer than the other the gambrel profile becomes distorted. 

The math to come up with this equality and generate the coordinates of the overall roof height and the pitch break is rather interesting and for those mathematically inclined is given below.  Note that the equation ends up being a quadratic equation with the positive root extraneous:





Another thing to consider with large spans (30ft. or greater) is the problem of truss height.  Every truss manufacturer I've ever gone to has truncated (piggybacked) my trusses at 13'-6".  Realistically this means that there is probably a limit to the span of a gambrel attic truss because of this height restriction and the geometry of this roof type.  As the height of  the pitch break approaches the 13'-6" height how do you actually fabricate the truss and make it work?

If anyone has an example of a gambrel attic truss with a pitch break higher than the typical cut off of 13'-6" I would really like to see it.
« Last Edit: November 06, 2015, 01:23:41 AM by Medeek »
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline MountainDon

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Re: Truss Calculators
« Reply #137 on: November 06, 2015, 07:08:10 AM »
I'm not that mathematically inclined. But I really do appreciate the work you put into this. Probably a lot of satisfaction from it.  [cool]
Just because something has been done and has not failed, doesn’t mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline Medeek

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Re: Truss Calculators
« Reply #138 on: November 06, 2015, 06:21:18 PM »
I'm working on the advanced options for roof trusses and I'm looking at the fascia board.  I've come up with three different configurations for the fascia that I've seen in practice and in the architectural books that I have. 

Which method of the three below do you prefer?  or is there another configuration that I have missed?

Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

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Re: Truss Calculators
« Reply #139 on: November 06, 2015, 09:00:54 PM »
4) typically I do #3 but you only drew the subfascia on the tail. Beyond the sub is a flush fascia bridged over by the drip edge. typically a 2x6 sub and a 1x8 fascia.

Offline Medeek

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Re: Truss Calculators
« Reply #140 on: November 06, 2015, 09:11:37 PM »
4) typically I do #3 but you only drew the subfascia on the tail. Beyond the sub is a flush fascia bridged over by the drip edge. typically a 2x6 sub and a 1x8 fascia.

I'm only going to draw the sub fascia and the sheathing.  Additional trim, flush fascia, drip edges, ridge vents, ridge caps or other features I will leave to the designer to draw.

In the advanced options I would like to included the following options:

1.) Sub Fascia
2.) Sheathing
3.) Rake/Barge Board
4.) Vent Blocking
5.) Outlookers (Structural vs. Non-structural, Horz. vs. Vert.)
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline garyc

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Re: Truss Calculators
« Reply #141 on: November 07, 2015, 07:25:06 AM »
What you are doing is great but most of it is way over my head. But still enjoying reading your thread. Hear is a web link that I like using for gambrel  trusses.  http://www.blocklayer.com/
If it wasn't for bad luck . I would 't have any luck at all.

Offline Medeek

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Re: Truss Calculators
« Reply #142 on: November 07, 2015, 08:09:21 AM »
What you are doing is great but most of it is way over my head. But still enjoying reading your thread. Hear is a web link that I like using for gambrel  trusses.  http://www.blocklayer.com/

I have looked at this gambrel calculator and I understand the logic behind it however it is too limiting.  What I mean by that is that certain combinations of upper and lower pitches are going to be missed by this arrangement.  Also the length of the two legs of the roof quickly become unequal which distort the gambrel shape.

I think it is better to let the user decide the pitch of each leg independently and then calculate the roof shape based on equal or nearly equal leg lengths.  To further generalize the solution I should probably include a ratio factor R = L1/L2 which can be set for values other than 1, this would provide a gambrel solution that would cover every conceivable configuration.

I will have to rework my equations in order to solve for X2 with the ratio factor R incorporated.
Nathaniel P. Wilkerson, P.E.
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Offline garyc

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Re: Truss Calculators
« Reply #143 on: November 07, 2015, 04:34:52 PM »
I some what understand what you are saying . But talking to older builders that built Barnes the old way the gambrel tresses is based on eight sided or octagon shape to maximum strength and equal pressure. I do under stand that wider the building the taller the truss will be . This is why a lot of truss company's don't build gambrel trusses. To wide to hall down the road. In my thread our build in Lincoln co. I was very pleads the way my barn trusses came out.   http://countryplans.com/smf/index.php?topic=13947.0 . Like I Sade I really enjoy reading your thread because there is not munch info out there for the home builder that wants to build there own trusses that can handle the dead load and snow load . I do appreciate you tanking the time and sharing all the hard work you been doing.    [cool] [cool]                       
If it wasn't for bad luck . I would 't have any luck at all.

Offline Medeek

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Re: Truss Calculators
« Reply #144 on: November 07, 2015, 05:56:02 PM »
Your right the "true" gambrel roof is the octagon rotated 22.5 degrees and then cut in half.  I haven't compared actual numbers to concretely say that this shape is the best for max. strength but I do not doubt it either, I would need to analyze this further.  The lower and upper legs are equal and the upper (4.971:12) and lower (28.971:12) pitches are the inverse of each other.  This is probably the simplest gambrel configuration to layout because of its symmetry.  The span is exactly double that of the  height.

Very nice build by the way.  I really need to get on the site more often just to look through some of these projects.  I like the wings added to the gambrel structure reminds me of the barn I grew up with in Terrace B.C. (Dad's potato farm).
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

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Re: Truss Calculators
« Reply #145 on: November 07, 2015, 06:22:00 PM »
Under advanced option 4, the vent blocking. Stuff you probably know. Code in the last few cycles has changed, or restated lateral bracing from elsewhere previously into chapter 8.
Quote
R802.8 Lateral support.
 Roof framing members and ceiling joists having a depth-to-thickness ratio exceeding 5 to 1 based on nominal dimensions shall be provided with lateral support at points of bearing to prevent rotation. For roof rafters with ceiling joists attached per Table R602.3(1), the depth-to-thickness ratio for the total assembly shall be determined using the combined thickness of the rafter plus the attached ceiling joist.

Exception: Roof trusses shall be braced in accordance with Section R802.10.3.

R802.10.3 defers to manufacturers bracing.

Offline Don_P

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Re: Truss Calculators
« Reply #146 on: November 07, 2015, 06:57:50 PM »
What do they call it, synergy... from flyingvans thread;
http://countryplans.com/smf/index.php?topic=11802.200
Id bet the highest strength combinations will fall around shapes that a catenary arch can be roughly inscribed within. You can play with a hanging chain and I'd bet it will show you the most efficient shapes. Then flip the shape over, when you do this what was pulling your arms apart to create a shallower and shallower arch becomes thrust trying to push the feet of the arch apart. Hmm, with that thought in mind it just might be strongest to build a gambrel I find ugly, one of the tall sided short topped ones.

Offline Medeek

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Re: Truss Calculators
« Reply #147 on: November 07, 2015, 07:01:24 PM »
Under advanced option 4, the vent blocking. Stuff you probably know. Code in the last few cycles has changed, or restated lateral bracing from elsewhere previously into chapter 8.
R802.10.3 defers to manufacturers bracing.

I've seen a few variations on blocking.  I think vertical blocks with angled tops is probably the most correct method.  Locally I usually see angled bird blocking.  Raised heels further complicates the matter. 
Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #148 on: November 07, 2015, 09:22:05 PM »
The raised heel trusses is mainly where I was thinking, that can get very tall and slender. I also like to block between rafters to keep windwash through the fiberglass down in a vented roof. Then it is a block with a gap between block top and sheathing for a vent channel. A detail on one plan had me cut a 1.5 x 5.5" notch in the top edge center of otherwise full height block. We did take his name in vain for a bit.

Offline Medeek

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Re: Truss Calculators
« Reply #149 on: November 07, 2015, 10:55:24 PM »
The SBC has a fairly lengthy discussion on heel blocking at this paper:

http://support.sbcindustry.com/images/technotes/T-HeelBlocking08.pdf

Raised heel trusses with large heel heights are given a "truss block" treatment.

However, APA paper SR-103A (2014) goes into some detail about using only the wall sheathing extended over the top plate in low wind speed areas.

The USDA has done some testing here:

http://www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr214.pdf

The heel blocking/bracing at heels of raised/energy trusses becomes more of an issue when a shearwall or braced wall panel is located beneath that segment of the wall line.

An article in the SBC Magazine:

http://www.sbcmag.info/article/2015/truss-blocking-panels

The 2012 IRC:

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_6_par055.htm

A paper that sums it up quite nicely:

http://smartgreenbuild.com/blog/download/519/

This was an interesting paper I have never seen before even though I subscribe to this publication:

http://www.structuremag.org/wp-content/uploads/2014/08/C-StructPerformance-Martin-Aug101.pdf
« Last Edit: November 07, 2015, 11:23:47 PM by Medeek »
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer